DNA repair systems identified in mitotic cells of the yeast Saccharomyces cerevisiae are being examined for their protection of cells undergoing meiosis and the role of the corresponding genes in normal meiosis. The RAD50, RAD52 and RAD57 genes are essential in the repair of DNA double-strand breaks in mitotic cells. We have shown that they are also required for meiosis. Mutations abolish normal meiotic recombination; RAD50 acts early in meiosis. Rare single-strand interruptions (SSIs) are observed in rad52 and rad57 strains which appear to be related to recombination and these have been characterized. Based on genetic and biochemical changes, the order of gene function appears to be RAD50, RAD52, and RAD57. Given the important role RAD52 plays in repair and recombination, we have initiated studies to characterize its function in normal DNA metabolism and following treatment with DNA damaging agents. This is being done by "domain mapping" the functional regions of the RAD52 gene and by examining its interactions with other genes. A complete deletion has been created and modified complementing and mutant versions of the RAD52 are maintained on a plasmid. Using this system in combination with a mutation in the DNA polymerase III gene, the RAD52 has been shown to be required during replication. The RAD52 gene product is also essential in repair and must be present prior to DNA damage exposure.